1. Field of the Invention
The present invention relates to a semiconductor device covered with a molding resin.
2. Related Art
FIG. 8 illustrates a semiconductor device according to the related art. A semiconductor device 500 includes an insulating substrate 51, a semiconductor chip 52 which is fixed to an insulating substrate 51, a bonding wire 55 which has one end connected to a surface electrode 52a of the semiconductor chip 52, an external lead terminal 56 to which the other end of the bonding wire 55 is connected, and a molding resin 57 which covers (molds) these components.
An aluminum insulating substrate or a ceramic insulating substrate is used as an insulating plate 51b of the insulating substrate 51. A circuit pattern 51a which is a cooper film is formed on the front surface of the insulating plate 51b and the semiconductor chip 52 is bonded onto the circuit pattern 51a by a bonding material 58 such as solder. In addition, a radiator plate 59 for dissipating heat generated when the semiconductor device 500 is used is fixed to the rear surface of the insulating plate 51b. The bonding wire 55 is used to connect the surface electrodes 52a of the semiconductor chip 52 and another semiconductor chip 52 which is provided separately from the semiconductor chip 52. The bonding wire 55 is also used to connect the circuit pattern 51a and another external lead terminal 56 which is provided separately from the external lead terminal 56. In many cases, the external lead terminal 56 is a plate-shaped lead frame and is made of a cooper material with high workability and conductivity. In general, for example, an epoxy resin is used as the molding resin 57.
In the molding-resin-type semiconductor device 500, the adhesion between the external lead terminal 56 or circuit pattern 51a which is made of a conductive material, such as a cooper material, and the molding resin 57 which is, for example, an epoxy resin is not high. Therefore, in some cases, immediately after molding, the molding resin 57 peels off due to contraction. In addition, even though the peeling-off of the molding resin due to contraction immediately after molding is prevented, the molding resin is likely to peel off due to a difference in thermal expansion coefficient between the molding resin and the cooper material when there is a temperature variation in the usage environment of the semiconductor device 500. In a semiconductor device with high current capacity, the width of a lead frame forming the external lead terminal 56 is large and the peeling-off of the molding resin occurs remarkably.
As a method for preventing the peeling-off of the molding resin, for example, there is a method illustrated in FIG. 9. That is, an anchor hole 61 which is a through hole is formed in an end portion of the external lead terminal 56 which is a lead frame. Then, the anchor hole 61 is filled with the molding resin 57 and a molding resin 57a and a molding resin 57b which are respectively arranged on the upper and lower sides of the external lead terminal 56 are connected to each other through the anchor hole 61. Therefore, an anchoring effect is exhibited and the adhesion between the molding resin 57 and the external lead terminal 56 is improved. As a result, the molding resin 57 is prevented from peeling off.
For example, in the method illustrated in FIG. 10, a conductor piece is provided as an anchor member 62 on an external lead terminal 56 which is a lead frame. Since the anchor member 62 is provided, the adhesion between the external lead terminal 56 and a molding resin 57 is improved and the molding resin 57 is prevented from peeling off.
In addition, there is a structure in which a plurality of concave portions are also formed in the circuit pattern 51a or the conductive piece is also provided as the anchor member on the circuit pattern 51a, in order to prevent the peeling-off of the molding resin.
For example, Japanese Patent Application Publication No. JP 2007-287800 A (also referred to herein as “Patent Document 1”) discloses a semiconductor device which includes an insulating substrate, a semiconductor chip, a bonding wire, a lead frame, a molding resin, and a lead frame having a concave portion formed in the surface thereof in order to prevent the molding resin from peeling off.
Japanese Patent Application Publication Nos. JP 2002-83917 A (also referred to herein as “Patent Document 2”) and JP 10-270629 A (also referred to herein as “Patent Document 3”) disclose a technique which performs etching or rolling on the surface of a material used for a lead frame to roughen the surface, thereby preventing a molding resin from peeling off.
Japanese Patent Application Publication No. JP 2005-183417 A (also referred to herein as “Patent Document 4”) discloses a technique which forms a structure which functions as an anchor member, that is, an aluminum wire bonded by stitch bonding, a metal plate bonded by ultrasonic bonding, a coated adhesive, a sheared structure, or a squeezed structure, in the vicinity of a fixing portion between a lead frame and a bonding wire to improve adhesion strength to the lead frame, thereby preventing the molding resin from peeling off.
Japanese Patent Application Publication No. JP 2009-49298 A (also referred to herein as “Patent Document 5”) discloses a semiconductor component in which an opening portion through which a portion of the surface of a semiconductor element is exposed is formed in a molding resin layer and an uneven portion is formed in the surface of the semiconductor element around the opening portion to prevent peeling-off or cracks at the interface between the semiconductor element and the edge of the opening portion in the molding resin layer.
However, in the method illustrated in FIG. 9 or the method disclosed in Patent Document 1, since the anchor hole or the concave portion (recessed portion) is provided, the cross-sectional area of the external lead terminal, which is a lead frame, is reduced. Therefore, when the amount of current which flows to the external lead terminal increases, there is a concern that heat will be generated from the external lead terminal 56, resulting in an increase in temperature.
In the method illustrated in FIG. 10 or the method disclosed in Patent Document 4, in some cases, the external lead terminal, which is a lead frame, is not partially bonded to the structure functioning as the anchor member due to thermal stress. When the non-bonded portion is generated, there is a concern that the molding resin 57 peels off from the non-bonded portion.
In the methods disclosed in Patent Documents 2 and 3, a surface roughening process is performed on the surface of the material used for the lead frame using etching or rolling in order to obtain the anchoring effect. However, the effect of preventing the molding resin from peeling off is not sufficient.
In the method disclosed in Patent Document 5, since the uneven portion is formed in the surface of the semiconductor element, there is a concern that the uneven portion will have an effect on the performance of the semiconductor element.